The Stirling engine, which is under development work for automotive applications, employs an external heating circuit which demands a high air flow mass therethrough for promoting proper thermal conditions to operate the engine efficiently. To obtain such air flow mass, a blower or compressor is required to force the air through a preheater matrix and into the combustion chamber and back again through the preheater matrix. In most state of the art automotive applications of the Stirling engine, the blower is connected directly to the output shaft or accessory shaft of the engine by way of a belt drive. This direct belt is typically designed with a blower to engine speed ratio which will give the required air delivery at idle engine speed. However, this usually results in a ratio (about 5.0:1.0) at idle; this ratio becomes excessive and more than what is required at higher engine speeds. At 600 r.p.m. engine speed, a 5.0:1 ratio is desirable; at 4000 r.p.m. speed the desired ratio typically becomes 3.5:1. The ratio must vary with engine speed. The large single ratio drive system results in excessive speed, noise and parasitic power consumption due to the driving of the blower at undesirable speeds and/or torques.
What is needed is a power transmitting system that can be interposed between the blower and the engine which will allow a change of speed ratio between the engine and blower that is generally inversely proportional to the output speed of the engine; the blower operation should be isolated from speed changes of the engine. This will require a power transmitting mechanism which (a) affords a wide variation in speed ratios, (b) is light weight and (c) is compact to suit the needs of automotive limitations and low cost.